Explanation of error OCL errors while evaluating derived attribute

There was an 'exceptional situation' (e.g. program exception) while evaluating OCL code.
The source of this error may be a bug with the Validator, but it might also be due to a
bug in the metamodel's (or profile's) OCL code. It might even be due to a fault in the
XMI exchange file being processed. (Every effort has been made to eliminate this last source.)
Detailed explanation of these errors in not yet provided because the explanations are so various
and can be complex. If you are really interested, ask in the MIWG.